SumoMe is not working in Hiero theme

Could you please let me know where i can find the header.php. I need to include one script in the header. please see below reply from Sumome.

reply from sumome
Is this a custom theme? Do you know if this theme uses wp_head() function to inject content into a global header? If you’re unsure you should contact your developer and ask. If you do not have a developer, contact the theme creators.

Hi, yes theme use wp_head() . You can find header.php if you go to Appearance > Editor (list of template files to the right).

I have added the script

<script src="//load.sumome.com/" data-sumo-site-id="f3dfdbc4169d9c258aac0c8dc083b9702e56e09169106e6838167e77abee134a" async="async"></script>

but it is not injecting.

Please can you post your page link?